I found my answer. :lol:
Cupreous Metal (Copper, Bronze, Brass) Conservation
http://nautarch.tamu.edu/crl/conservationmanual/File12.htm
From it:
The first step in the electrochemical corrosion of copper and copper alloys is the production of cuprous ions. These, in turn, combine with the chloride in the sea water to form cuprous chloride as a major component of the corrosion layer:
Cu -e >> Cu+
Cu+ + Cl- >> CuCl
Cuprous chlorides are very unstable mineral compounds. When cupreous objects that contain cuprous chlorides are recovered and exposed to air, they inevitably continue to corrode chemically by a process in which cuprous chlorides in the presence of moisture and oxygen are hydrolyzed to form hydrochloric acid and basic cupric chloride (Oddy and Hughes 1970:188):
4CuCl + 4H2O + O2 >> CuCl2 · 3Cu(OH)2 + 2HCl
The hydrochloric acid in turn attacks the uncorroded metal to form more cuprous chloride:
2Cu + 2HCl >> 2CuCl + H2
The reactions continue until no metal remains. This chemical corrosion process is commonly referred to as 'bronze disease.' Any conservation of chloride-contaminated cupreous objects requires that the chemical action of the chlorides be inhibited either by removing the cuprous chlorides or converting them to harmless cuprous oxide. If the chemical action of the chlorides is not inhibited, cupreous objects will self-destruct over time.
Copper objects in sea water are also converted to cuprous and cupric sulfide (Cu2S and CuS) by the action of sulfate-reducing bacteria (Gettens 1964:555-556; North and MacLeod 1987:82). In anaerobic environments, the copper sulfide products are usually in the lowest oxidation state, as are the ferrous sulfides and silver sulfides. After recovery and exposure to oxygen, the cuprous sulfides undergo subsequent oxidation to a higher oxidation state, i.e., cupric sulfide. The whole chemical reaction generally proceeds along the same lines as those described earlier for iron.
Upon removal from a marine encrustation, copper and cupreous artifacts are inevitably covered with varying thicknesses of a black powdery layer of copper sulfide that imparts an unpleasing appearance. Occasionally, the corrosion process will pit the surface of the artifact, but this is more common on cupreous alloys where tin or zinc is corroded preferentially. The stable copper sulfide layer does not adversely affect the object after recovery from the sea as do copper chlorides; copper sulfides only discolor the copper, imparting an unnatural appearance to the metal, and are easily removed with commercial cleaning solvents, formic acid, or citric acid. (See North and MacLeod [1987] for a detailed discussion of the corrosion of copper, bronze, and brass in a marine environment.)
